The present invention relates generally to products and methods for providing fall protection systems for construction workers, maintenance workers, inspectors and others who work or walk upon elevated structures. More particularly, it relates to fall protection systems which employ safety stanchions mounted to the elevated structure so as to anchor and support safety cables (commonly known as horizontal lifelines).
It is common for workers to work and walk upon the roofs (which include large commercial skylights) of commercial buildings, which are flat and of varying slopesxe2x80x94some of which are quite severe. Obviously, it is important but often difficult to protect such workers and others from harm if they happen to slip and fall off the roof. It is common during the construction phases and during repair and replacement of roof structures, that the roof surface will have holes in the interior sections of the plane of the roof. Thus, falls to the interior of the building as well as off the edge of a roof are ever present dangers.
It is also important, for the purpose of controlling costs, that any fall protection system which is put in place to protect the workers be relatively inexpensive and easy to install and cause little interference with the work being carried out by the workman. Further, the fall protection system should also preferably be adaptable to virtually any roof, whether the roof is very rigid and uses more massive structural components such as those made with structural beams and joists, or the roof is relatively lightweight and designed for movement or flexion (such as a large skylight canopy), or the roof is for a lightweight metal building, which are characteristically made with lighter weight rafters and purlins. Some roof systems employ poured concrete on top of metal decking, and it would be desirable if a fall protection system were mountable to these systems as well.
Most conventional fall protection systems to which the present invention relates involve systems for supporting the worker (after a fall) with a safety cable that may be anchored and supported in various ways. Once a safety cable is anchored and supported, workers may be assured that they will be suspended in the case of a fall by attaching themselves to the safety cable, as, for example, by way of a safety lanyard attached both to the cable and to a harness worn by the worker. However, virtually all such systems involve heavy structural attachments that penetrate the roof surface to attach to structural metal below and are also rigid and unyielding. This makes such systems undesirable and extremely expensive to install if a building owner wishes to retrofit his building with system after the structure has been erected, due to the potential for damage to interior tenants, and water infiltration during construction among other inconveniences typical to a significant remodeling project.
Moreover, after a fall arrest, a typical system is taken out of service, and it is likely that the safety stanchion posts of the system will have to be removed, inasmuch as the post as well as the mounting will have been subjected to severe forces and therefore are likely to have suffered damage. Obviously, replacement of the stanchions is objectionable for the same reasons described earlier with respect to the initial installation of such systems. Replacement is also objectionable due to the additional costs and potential damage to the building as a result of the repair.
Other conventional systems (such as that described in U.S. Pat. No. 5,287,944 to Woodyard) (which is commonly employed only during construction of wood roofs) employ a large obtrusive plate that keeps the cable so low and slack so as to lay and flop against the roof surface. This is unacceptable to builders, manufacturers, and owners of finished long life roof systems made of coated sheet metals and glass. If a structure such as Woodyard""s were increased in height the increased leverage would likely rip it off the roof, thus rendering it unreliable as well as larger and harder to attach and potentially causing more damage during installation. Indeed, a cable that is not adequately supported is potentially dangerous since it is likely to bang violently against the glass plates during a wind storm and potentially fracturing the glass and injuring people. If the cables are tightened, (for instance to get rid of some sag) the forces go up so significantly that the tension in the cable alone could cause damage to many roofs, even before the massive forces of a fall arrest event are applied. Therefore, it can be seen that there is a need for a system that has some height so as to keep the cable supported and off the roof; some means to support the cable at intermediate points that are not obtrusive nor expensive; does not require penetration of the roof structure; is aesthetically pleasing; allows for cable sag (or does not require cable tensioning) for reduced forces (but not so much that the cable begins to cause damage to the fragile glass, metal or other roof material); reduces forces by using sacrificial members and allows the cables to be lowered during a fall arrest to reduce leverage and force at the end pointsxe2x80x94with the feature of having the sacrificial parts easily replaceable without having to further disturb the roof system and penetrate the building which exposes the tenants and the owners to potential damage and delay. Further, the system is preferably lower cost and easier to install due to surface mounting rather than requiring significant penetration of the roof to install.
Unfortunately, in many commercial buildings such as those of the type known as system metal buildings (also known as pre-engineered metal buildings or xe2x80x9cButler buildingsxe2x80x9d) and large commercial skylights and canopies, workman must walk and work upon these sloped roofs where there are few or no suitable anchoring points for attaching safety cables. Many manufacturers of these structures do not have the expertise to design fall protection systems and many shy away from the liability, assuming safety systems are complex and require significant maintenance. Most commercial buildings in service today, and even those currently under construction still do not have any type of safety or fall protection roof structure installed.
A previous invention of which I am a co-inventor and which is described in U.S. Pat. No. 6,173,809 provides a safety stanchion for mounting upon a surface such as structural I or H shaped beam which are typically found in the superstructure of a bridge, a building or some other structure being built.
This safety stanchion includes a tapered tubular post having a lower end for attachment to a support base at preferably an oblique angle and an upper end for supporting a safety cable and the like. Due to its tapered shape, the post""s upper end has an outside diameter which is less than that of its lower end. The post also preferably has a wall thickness of less than 0.125 inches and is frustoconically shaped. In addition, the post is preferably made out of an energy absorbing, elastic-like, high strength steel such as A595 grade steel which in cooperation with the post""s wall thickness and tapered, preferably frustoconical, shape is believed to render the post capable of inelastically deforming before it fails, thereby better able to break a worker""s fall without actually breaking in half. Fail or failure of the post as used herein refers to a post which has actually broken or buckled to a point where it is no longer capable of providing any significant resistant to lateral forces or other forces tending to cause bowing of the post.
In the preferred safety stanchion of this type, the tapered post is capable of flexing and permanently (or inelastically) deforming without failing, in response to sudden loads (within its design limits) that might occur when a person who is attached to the stanchion (or a cable suspended between two stanchions) via a lanyard falls from an elevated beam or similar surface upon which the stanchion is mounted.
While the invention of the ""809 patent is easily attachable to I beams and other structural members, a need still exists for safety stanchions and safety stanchion systems which are attachable to sloped roofs, particularly those of the type which are supported by crisscrossing rafters and purlins, are lightweight sheet metal, and commercial skylights that are commonly made of lighter weight materials.
In addition to roof surface attachability, there is a need for a system that is simple, low profile so as to be aesthetically pleasingxe2x80x94or at least be aesthetically unobtrusive when installed on decorative roofs and skylights, and made of materials that are low maintenance and long lasting. The system ideally has easily replaceable parts that because of sacrificial shock absorbency enable components to be salvaged after a fall arrest and which after replacement allow the fall protection system to placed back in service in a short period of time without extensive new construction or repairs to the mounting means or the system""s major components.
The present invention builds upon the invention of the ""809 patent and the prior art by providing a unique safety roof structure including unique safety stanchion apparatus"" for mounting directly to the roof of a building, particularly those typically found in commercial buildings and skylights and supported by crisscrossing rafters and purlins.
One unique safety stanchion of the present invention includes a post having first and second ends, means for supporting a safety cable at said first end of said post and a base at the second end of the post for mounting the post on a generally flat surface portion of a flat or sloped roof or glass skylight supported by crisscrossing rafters and purlins.
In a preferred embodiment of this safety stanchion, the base includes a mounting plate having a cross shape for aligning with and being supported by the crisscrossing rafters and purlins of the roof structure supporting a generally flat sloped roof. The mounting plate is attachable to at least one of said crisscrossing rafters and purlins. However, if the rafters are strong enough, the cross shaped mounting plate may be replaced with a simple elongated plate for attachment solely to the rafter. In these embodiments, any or all of the post, base and means for supporting a safety cable at said first end of said post means may be sacrificial in the sense that is capable of inelastically deforming or bending without failing during a workman""s fall as such is described in the ""809 patent.
The present invention as set forth in the claims appended hereto also provides a unique safety roof system or structure which includes crisscrossing rafters and purlins for supporting a roof or glass skylight surface and a plurality of the aforementioned safety stanchions.
The present invention also provides another unique safety roof system which additionally includes a structural member for supporting a rafter (also sometimes referred to as a beam) which defines an opening extending through the rafter. This roof structure also includes a plurality of safety stanchions. However, the stanchions of this roof structure differ from that previously described in that the stanchion is provided with an elongated rigid base that extends through the opening provided in the rafter and is attached at its lower end to the structural member supporting the rafter.
The post of this stanchion may also be sacrificial in the sense that is capable of inelastically deforming or bending without failing during a workman""s fall as such is described in the ""809 patent. In addition, the second or lower end of this sacrificial post is preferably removably fastened to the upper end of the rigid elongated base. This allows the post to be easily removed and replaced if it becomes deformed as a result of a workman""s fall and allows the base to remain for the life of the roof structure, virtually unaffected by successive falls upon the sacrificial upper end pieces. Any common post which does not have this feature is likely to cause so much strain on the roof (due to the raised lever action common to most posts) that a fall will cause damage to the roof structure and after a fall is likely to be out of service for extensive periods of time while roof construction or repair specialists are recruited to repair the damage caused and to replace the stanchions. Also and as with most safety stanchions, the post defines or has attached to its first or upper end a means for supporting a safety cable which may simply consist of a hole defined by the post""s upper end to which the safety cable is attached. This roof structure may also include a plurality of the aforementioned safety stanchions having cross-shaped bases and when so used in combination provide multiple benefits including allowing cables to be positioned relatively low over the top of the roof structure while still preventing the cable from damaging glass skylights or painted sheet metal (for example when the wind buffets the cables), rendering an area of the roof safe for users to tie off and ease of tie off with a slightly elevated cable, while being capable of sacrificially bending to reduce forces on a worker and reducing the forces on the base and thereby assuring with some certainty that the roof structure is not damaged. Further, the grouping of a series of posts and end attachments into separate systems (a series of posts and sacrificial end attachments as opposed to a single long lifeline with only two terminations) allows more than one set of workers to perform work with another set of workers, each pair (typically two to three workers per system) being attached to different safety lines. In the event one worker falls and his partner where to be pulled off or fall with him, the adjacent sets of cables could be used to provide fall protection for other workers to rescue the fallen workers. Other benefits of multiple bases include force reduction and reduced lifeline loading (generally more posts will reduce lifeline forces), while the pass-through design allows continuous movement of the workers without the aggravation of hooking a second lanyard over the top of an intermediate point before disconnecting a previously attached first lanyard. The multiple intermediate series of posts also allows for clearance of the cable above the glass skylight or other roof material while allowing for sufficient horizontal lifeline sag which again adds some shock absorbency and reduces force factors. Finally, the system supplies the support needed to make the system effective, safe, and aesthetically pleasing.
The present invention also provides a safety stanchion apparatus that can be mounted to a flat surface on virtually any roof. This safety stanchion has a rigid and generally nondeformable base but the stanchion""s post or its cap or means for supporting the safety cable is removable and capable of inelastically deforming before failing. This enables a deformed (i.e. sacrificed) component of the stanchion to be replaced without having to replace the entire stanchion which is not only expensive but also more difficult and unsafe than simply replacing a component (post or cap) of the stanchion. The base also has a generally flat underside surface for attachment to a generally flat section of a roof.